Scrubber

ABSTRACT

A scrubber comprises a casing (1) with an inlet (2) and an outlet (3) for flue gases, and with an outlet (4) for water and substances separated from the flue gases, and water injection nozzles. The casing (1) is divided, by means of a partition having a throughflow opening for flue gases, into an evaporation zone (11) in which injected water is caused to cool the flue gases by heat absorption and evaporation, simultaneously as the water adsorbs any substances carried along by the flue gases, and a condensation zone (12) in which flue gases and steam from said first zone are condensed. The flue gas outlet from the condensation zone is provided with a drop separator (8), and the partition (151) separating the two zones is arranged as a collector of water which has not evaporated in said evaporation zone and which by means of a pump (16) and further nozzles (17), is reinjected into said evaporation zone (11).

The present invention relates to a scrubber. More particularly, theinvention relates to a scrubber for recovering the energy in hot fluegases and simultaneously reducing the moisture content of the dischargedcooled flue gases and separating any substances carried thereby.

Because of the ever-growing fuel costs, and in spite of more efficientheating plants and control systems, it has become increasingly importantto make available heat recovery systems affording a better utilisationof the energy content of the fuel, thereby to reduce the total cost of,for example, house heating. Besides, the increasing environmentalpollution has stimulated the development of systems for separatingpollutants from the flue gases emitted by heating plants. Heat recoveryand flue gas purification are preferably carried out simultaneously in aso-called scrubber.

However, prior art scrubbers suffer from several disadvantages. Forexample, the moisture content of the discharged and intensely cooledflue gases is frequently far too high and may cause corrosion in thechimney or the smoke pipe. To eliminate this problem, the flue gasesmust therefore be reheated, and this requires a certain amount of energywhich is obtained from a separate source of energy. If, on the otherhand, the flue gases are not intensely cooled in the plant, their energycontent will be recovered less effectively, simultaneously as themoisture content may still be high and cause corrosion. Specialfacilities must therefore be provided for reducing the moisture content.

It therefore is the object of this invention to obviate thedisadvantages of prior art scrubbers and to provide a scrubber whicheffectively recovers the energy content of the flue gases and maintainsthe moisture content of the discharged flue gases at a low level. Thisis achieved by heating the discharged flue gases by heat exchange withthe incoming hot flue gases, and by recovering the energy content of thehot flue gases by heat exchange and water injection in an evaporationzone by means of an arrangement which ensures adequate evaporation ofthe injected water, and in a condensation zone in which the water vapouris condensed. To this end, the scrubber of the present invention hasbeen given the characteristic features stated in claim 1.

The invention will now be described in more detail below, referencebeing had to the accompanying drawing which is a schematiccross-sectional view of the scrubber according to the invention.

In its preferred embodiment, the scrubber according to the inventioncomprises a casing 1 having an inlet 2 for hot flue gases from, forexample, a heating plant (not shown), an outlet 3 for discharged, cooledand purified flue gases, said outlet being connectible to a chimney orthe like, and an outlet 4 for condensate, water and separatedpollutants. An internal smoke pipe 5 connected to the outlet 3 extendsthrough the centre of the casing 1.

The lower end of the smoke pipe 3, which is positioned near thecondensate outlet 4, comprises a widened portion 7 which serves as adrop separator 8 and preferably is in the form of a coke bed. At its endconnecting with the outlet 3, the smoke pipe also has a widened portion6 whose function will be described later. Below the widened portion 6, aheat exchanger 9 is arranged which is shown schematically and adapted torecover, when need arises, part of the heat content of the flue gases.

Along its inner side, the casing 1 is provided with a number of nozzles10 through which water from an external system is injected by means of apump 101. It should here be added that the interior of the casing isdivided, by means of partition to be described later, into anevaporation zone 11 and a condensation zone 12. The water injectedthrough the nozzles 10 has a relatively low temperature and is heatedand evaporated in the evaporation zone 11, while simultaneously loweringthe temperature of the flue gases and adsorbing the pollutants therein.The cold water injected into the condensation zone 12 contributes torecovering the energy content of the flue gases and, by condensation,the energy content of the water vapour coming from the evaporation zone11 and carried along by the flue gases.

The widened portion 6 of the smoke pipe contains a turbulator 13 whichcan be provided with a helical flange 14 or the like to improve theturbulence in the discharged flue gases. The widened portion 6 and theturbulator 13 therein also constitute a heat exchanger for heat exchangebetween the hot flue gases that have entered through the inlet 2 andflow around said portion 6, and the cooled flue gases discharged throughthe outlet 3. The flange 14 promotes the heat exchange between the hotand cold flue gases by forcing them in an outward direction. The heatexchanger causes the cooled flue gases flowing upwardly in the pipe 5and having a relative air humidity of almost 100 percent and atemperature of about 15° C. to be reheated to about 25° C., whereby therelative air humidity of the flue gases is reduced to below 50 percent.In this manner, the corrosive action of the cold and relatively humid,discharged flue gases occurring in prior art arrangements thus isavoided.

For better energy economy and to improve the evaporation of water in theflue gases, a water collecting device 15 is provided between theevaporation zone 11 and the condensation zone 12. The collecting device15 is formed by the partition 151 separating the evaporation zone 11from the condensation zone 12 and has a central throughflow opening forflue gases and water vapour. The opening is surrounded by an upstandingcollar 152, and above the opening a conical baffle 153 extends beyondthe edges of the collar and guides nonevaporated water drops outside thecollar such that the water is collected on the partition 151. The waterwhich has collected on the partition and is injected into theevaporation zone 11 through the nozzles 10, is reinjected by means of acirculation pump 16 and nozzles 17 in the evaporation zone 11. Thenozzles 17 are distributed throughout the evaporation zone 11, such thatwater jets are directed against the incoming flue gases which thus arecooled, simultaneously as the water is evaporated to a large extent.Water jets are directed also against the heat-absorbing surfaces to keepthese surfaces clean and to form a water film which facilitates heatabsorption. Because the recycled water has already been heated, thelarge absorption area gives a higher scrubbing action. The recirculationwater in the evaporation zone 11 which is collected by the partition 151will have a temperature above the dew point of the flue gases.

The scrubber according to the present invention operates as follows. Hotflue gases from a furnace, having a temperature of e.g. 250° C., enterthrough the inlet 2 in the casing 1 and come into contact with thewidened portion 6 serving as heat exchanger. By heat exchange withcooled flue gases flowing within the portion 6, the temperature of thegases just entered is slightly lowered, while the temperature of thedischarged flue gases is raised, simultaneously as the relative airhumidity thereof is lowered. Part of the energy in the flue gases canthen also be recovered in the heat exchanger 9.

In the evaporation and condensation zones 11 and 12, the flue gastemperature is lowered, by the injection of water, to about 15° C.,simultaneously as the pollutants in the flue gases are adsorbed by thewater and separated from the flue gases. Injected water that hasevaporated in the evaporation zone will here be recondensed to dropshape. In the water or drop separator 8, the water is separated from theflue gases and discharged through the outlet 4. The energy content ofthe heated consumed water is recovered in some suitable manner, forexample in the evaporator section of a heat pump (not shown). After thepollutants have been separated, the cooled water is recycled by means ofthe pump 101 to the nozzles 10 for renewed injection. Before they reachthe outlet 3, the cooled flue gases which, after passing through thedrop separator, are saturated with moisture, pass through the heatexchange portion 6 where they are heated. The outflowing flue gases thenhave a relatively low air humidity and can be discharged withoutdifficulty through the chimney.

A preferred embodiment of the invention has been described above withreference to the accompanying drawing. Naturally, a number ofmodifications can be made without departing from the inventive concept.For example, the briefly mentioned heat exchanger 9 may comprise severalheat exchangers located at different points around the smoke pipe 5 andalso around the widened portion 6. Furthermore, the turbulator 13 andthe flange 14 may be replaced by other means conducting the flue gasestoward the heat exchange surface between hot and cold flue gases andproducing a turbulent flow in order to promote heat exchange. Also theconstruction of the partition 151 may vary.

The invention is not restricted to the embodiment described above andillustrated in the drawing but may be modified in different ways withinthe scope of the appended claim.

I claim:
 1. Scrubber comprising a casing (1) with an inlet (2) for fluegases, nozzle means for injecting water into said casing, an outlet (3)for flue gases, and an outlet (4) for water and substances separatedfrom the flue gases, said inlet (2) and said flue gas outlet (3) beingarranged at the same end of the casing, and the condensate outlet beingarranged at the opposite end of said casing, and a smoke pipe (5) ofvarying area extending through said casing (1) up to said flue gasoutlet (3) from the casing end having the condensate outlet (4), awidened portion (6) of said smoke pipe (5) forming a heat exchanger fortransfer of heat from the incoming flue gases to the outgoing cooledflue gases, characterised in that the scrubber casing (1) is divided, bymeans of a partition (151) having a flue gas throughflow opening, intotwo spaces or zones (11, 12); that cold water injection nozzles (10) areprovided in both of said zones for cooling the flue gases andevaporating the injected water in an upper such zone (11) provided inconnection with the flue gas inlet, simultaneously as the water adsorbsany substances carried by the flue gases, and for condensing watervapour carried by the transferred flue gases and cooling the flue gasesin a lower zone (12) provided in connection with the condensate outletand an intake end of the smoke pipe (5); that the partition (151)separating the evaporation zone (11) from the condensation zone (12) isadapted to collect any nonevaporated water in said evaporation zone (11)and has a drain pipe which, via a recirculation pump (16), is connectedto further water injection nozzles (17) in said evaporation zone (11)for reinjection of water already heated in said zone (11); and that theend of the smoke pipe (5), positioned in said condensation zone (12) andprovided with a widened portion (7), comprises a drop separator (8) forseparating water in liquid form from the flue gases which enter thesmoke pipe (5) and which, when passing another widened smoke pipeportion (6) arranged at the flue gas inlet and serving as heatexchanger, are again supplied with heat reducing the relative humidity.